Electric switch

Abstract

An electric switch 11 has contacts 12 and 13 which are initially closed by activating means 14. The invention provides urging means 22 to bias the switch against reopening of the contacts during at least an initial period which is useful if the activating means does not operate for long enough for the electric switch to assume its stable closed position. The urging means is responsive to current carried through the contacts. It is possible to provide a plurality of switches responsive to the same urging means, different switches being provided for different electrical circuits and possibly energised from different sources.

I claim: 
     
       1. A switch assembly comprising a pair of contacts having an open state and a closed state, means for activating the switch to move the contacts from the open state to the closed state and biasing means responsive only to only the current carried through the contacts providing positive reinforcement of the activation means for biasing the contacts against opening activation means for biasing the contacts against opening. 
     
     
       2. A switch assembly as claimed in claim 1 wherein the pair of contacts form part of a magnetic reed switch, the biasing means comprising a coil around contacts and connected in series with the contacts to create a magnetic field to the reed switch to urge the reed switch towards its closed state. 
     
     
       3. A switch assembly claimed in claim 2 wherein two said reed switches are provided, each responsive to the same activating means. 
     
     
       4. An assembly as claimed in claim 3 wherein the two switches are connected in parallel. 
     
     
       5. An assembly as claimed in claim 3 wherein one said switch is connected in series with the biasing means and the other said switch is connected to a load. 
     
     
       6. An assembly as claimed in claim 4 wherein said switches are connected to the same source for energisation. 
     
     
       7. An assembly as claimed in claim 4 wherein one said switch is connected to a main energising source and connects a load to the energising source and the other said switch is connected to a supplementary energising circuit. 
     
     
       8. An assembly as claimed in claim 7 wherein the supplementary energising circuit comprises a trickle charged capacitor which can be discharged through the biasing means on closure of the switch. 
     
     
       9. An assembly as claimed in claim 8 wherein the activating means comprises a magnetic flux circuit including an inertia body of magnetic material which is moved relative to the remainder of the magnetic flux circuit in response to an acceleration, thus causing a variation of the magnetic flux elsewhere in the magnetic circuit.